In-vivo studies of the menstrual cycle present enormous challenges, as they deal with a complex entity which is the result of multiple interactions between a large number of variables, not all of which can be controlled at one time in an in-vivo setting. Adjunct or alternative approaches to the in-vivo study of the human reproductive cycle have been suggested, among which is the computer simulation approach. This research proposal represents an attempt to evaluate the validity of this approach. The investigators propose to resume their studies with a computer model of the cyclic morphological and endocrine changes which characterize the menstrual cycle. The proposal contains three practical aims. The first aim is to refine the original menstrual cycle computer simulation model. This model was developed more than a decade ago; new data and concepts must now be evaluated, tested and, where required, integrated into the model. The second aim is to develop a sophisticated user interface. The model will be adapted to PC desktop type computer hardware and will incorporate principles of what are called "expert system" programs. This will allow physiologists to test and use the computer model in a highly sophisticated, yet easily controllable fashion without the need for an extensive computer background. The third aim is to test the utility of this computer modeling approach in an experimental setting. Selected experimentalists will provide us with an experimental setting. Selected experimentalists will provide us with an objective analysis of the model through their ability to log simulation results. Ultimately, a refined and validated model of the menstrual cycle can be used to assist in both experimental design and result interpretation and thereby enhance knowledge gained from in-vivo experimentation.